The present invention relates to an aftertreatment apparatus for imagewise exposed printing plates. More particularly, the present invention relates to an apparatus for aftertreatment of imagewise exposed printing plates comprising an exposure station which is inserted upstream of a heating station in which there is disposed in a housing lined on three sides with an insulation, an IR radiation source which radiates downwards through the housing, which is open at the bottom, and onto a reflector table over which the printing plate passes through the aftertreatment apparatus.
Such an apparatus is disclosed in EP-A-0 450 486 (DE-A 40 11 023), but makes use of a fluorescent lamp having a color filter placed in front of it in the exposure station. Upon ageing, however, a spectral alteration develops which has a disadvantageous effect on the optimum exposure of the printing plates since the latter occurs only in a narrow spectral range.
From DE-B 12 14 085 (U.S. Pat. No. 3,144,331) it is known to restore the sensitivity of photopolymerizable recording materials, which have been applied as a photosensitive layer to a printing plate support and whose sensitivity has fallen as a result of absorption of molecular oxygen, by exposure to 70 to 98% of the radiation dose of an actinic radiation which would be necessary to initiate a photopolymerization with uniform incidence. The exposure is carried out through the printing plate support, which is, for example, transparent, an actinic radiation being used which has a wavelength such that only 10 to 70% of the radiation is absorbed by the photopolymerizable layer. In this process the exposure is in principle first diffuse and then imagewise. The preexposure is carried out with lower intensity, namely with 70 to 98% of the radiation intensity which is necessary to achieve the full exposure action. This preexposure is then followed by the imagewise exposure with full radiation intensity.
U.S. Pat. No. 4,298,803 describes a process in which a photoresist layer is preexposed with an intensity which is lower than the critical exposure intensity at which the photoresist can be largely dissolved away at the exposed points. After this preexposure, the imagewise exposure of the photoresist layer takes place. The sequence of the two exposures can be interchanged. In both cases, the photosensitivity of the photoresist layer is improved, as a result of which the processing time is considerably shortened. In the apparatus used for this process, both the imagewise exposure and the preexposure or afterexposure of the photoresist can be carried out by means of an electron beam, or by a UV or X-ray source.
U.S. Pat. No. 4,716,097 likewise discloses a process in which a photopolymeric layer containing a dyestuff is first diffusely and then imagewise exposed with light having a wavelength above 400 nm and an intensity of at least 1500 lumens/m.sup.2.
German Offenlegungsschrift DE-A 24 12 571 discloses a process for curing a light-curable polymer layer of a printing plate, in which exposure is first carried out diffusely for a short time and then imagewise until the polymer layer is virtually completely cured in the exposed areas. The diffuse exposure duration is not more than 90% of the time within which the complete curing of the polymer layer takes place with equal intensity of the radiation both for the preexposure and for the imagewise exposure.